Journal of Biology, Agriculture and Healthcare ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) Vol 2, No.1, 2012
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responsible. The ethnobotanical uses of this mushroom to heal both plant and human diseases have been accumulated but scientific evidences are not yet well known. The main focus of present study lies in the investigation of a white-rot fungus- S. ostrea isolated from wood logs and their inhibitory activity against selected Gram-positive and Gram-negative bacteria. 1.1 Materials and Methods The white-rot fungus S. ostrea (Blume & T. Nees:Fr.) Fr. was kindly supplied by Prof. M.A. Singaracharya, Department of Microbiology, Kakatiya University, Andhra Pradesh, India and was isolated from wood logs. Two Gram-negative bacteria such as Klebsiella pneumoniae, Pseudomonas aeruginosa, and three Gram-positive bacteria such as Bacillus subtilis, Staphylococcus aureus and Micrococcus sps. were used in this study were obtained from Department of Botany, Sri Krishnadevaraya University, Anantapur, Andhra Pradesh, India. The strains of bacteria were maintained on nutrient agar medium at 370C for 24 h. 1.1.1 Antimicrobial Activity The fungus Stereum ostrea was cultured in Koroljova broth (Koroljova et al. 1984) and was incubated at 300C on rotary shaker at 150 rpm for 6 days. After incubation the liquid culture was filtered through two layers of Whatman No. 1 filter paper. Methanol extract was prepared by taking 1g of S. ostrea biomass, which was mixed with 50 ml of absolute methanol for 2 days. Later the solution was collected and filtered through several layers of Whatman No. 1 filter paper and collected the filtrate for its antibacterial activity. 1.1.2 Assay for antibacterial studies Antibacterial activities of crude as well as methanol extract were evaluated against selected bacteria. Fresh overnight cultures of inoculum (0.1 ml) of each culture containing 108 cells, was spread on agar plate. Three sterile paper discs (5mm diameter) were placed in each agar plate and on two discs crude, methanol extract of each 50µl was placed. On the third, absolute methanol was placed as a control. Ampicillin at 50ppm was placed as a positive control and distilled water was used as a negative control in all plates inoculated with selected bacteria. The bacterial cultures were incubated at 37°C for 24 h. The microbes were plated in triplicates and average zone diameter was noted in mm. 1.1.3 Determination of minimal inhibitory concentration The minimal inhibitory concentration was aimed to find out the lowest concentration of the sample that inhibits the growth of tested microorganisms. The samples were used against 2 Gram-negative and 3 Gram-positive bacteria. The test was carried out using filter paper disc method by using different concentrations (10-50 µl) of crude and methanol extract. Three sterile Whatman paper discs (5 mm diameter) were soaked each with 10, 20, 30, 40 and 50 µl of the aliquots of crude and methanol extract and placed on bacteria (106 CFU/ml) seeded plate. Bacterial cultures were incubated at 370C for 24 h. After incubation of all cultures, zone of inhibitions of bacterial growth were observed. Each experiment was done in 3 replicates and average zone diameter was measured in mm. Controls were maintained with devoid of
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